Pulsed oscillators



April 0, 1956 J. s. HARRIS 2,741,701

FULSED OSCILLATORS Filed Oct. 1, 1953 INVENTOR.

JHMES. S. HHRRIS United States Patent F PULSED OSCILLATORS James S. Harris, Old Greenwich, Conn., assignor to Radic Corporation of America, a corporation of Delaware Application October 1, 1953, Serial No. 383,584

Claims. (Cl. 25036) This invention relates to pulsed oscillators, and more particularly to improved pulsed oscillators which provide undamped oscillations and which do not require frequent adjustments to provide transient-free stopping of the oscillations.

A pulsed oscillator is one which generates oscillations during the periods it is switched on by an input pulse wave. Pulsed oscillators are used in systems requiring precise time measurement of intervals, under conditions where the intervals are not necessarily periodic, and where the starting times of the intervals are not predictable. These requirements exist in radar, loran, printing telegraph and other systems. In printing telegraph systems, a pulsed oscillator is used in a regenerative repeater which analyzes a degraded received pulse wave and regenerates the pulse wave sent from the distant point.

Pulsed oscillators should be capable of being turned on with a transient-free start and turned ofi with a transient-free stop, and they should oscillate at constant amplitude during the period that they are turned on. Prior art pulsed oscillators have not been capable of a completely transient-free stop, have not been capable of generating sustained oscillations of constant amplitude, and have required frequent operating adjustments to minimize the transients occurring when the oscillations are stopped.

It is an object of this invention to provide an improved pulsed oscillator capable of generating oscillations which are stopped without transient effects.

It is another object to provide an improved pulsed oscillator capable of generating sustained oscillations of constant amplitude.

It is a further object to provide an improved pulsed oscillator not requiring frequent adjustments to minimize stopping transients due to aging of the tubes.

In one aspect the invention comprises a tank circuit or a ringing circuit tuned to the frequency at which it is desired to generate oscillations. Normally, when no oscillations are desired, current is drawn thru the ringing circuit, thru a control tube which is conductive by reason of an appropriate voltage applied to its grid, and thru a cathode resistor. The low impedance of the control tube and the power supply is shunted across the ringing circuit to prevent oscillations. When the control tube is cut-ofi by the application of an appropriate voltage to its grid, the energy in the inductor of the ringing circuit starts oscillations in the circuit. A cathode follower is connected to the ringing circuit in such a way as to feed back into the ringing circuit suflicient energy to maintain constant amplitude oscillations therein. A stabilizing tube has its grid connected to a point of constant bias potential, and has its cathode connected to the cathode of the control tube so that the two tubes utilize a common cathode resistor. The stabilizing tube and the control tube are connected so that when one is conducting, the other is cut-off, and vice-versa. The common cathode resistor is large making the control tube a constant current device so that it draws a constant charging current 7 2,741,701 Patented Apr. 10, 1956 ice thru the ringing circuit when there are no oscillations in the ringing circuit. Therefore, the ringing circuit always starts oscillating at a predetermined amplitude of oscillations. The stabilizing tube prevents the cathode of the control tube from falling when the control tube is cut-ofi to permit oscillations in the ringing circuit. Therefore, only a moderate voltage drop on the grid of the control tube is necessary to cut the tube off.

In another aspect the invention includes a diode arrangement in the plate circuit of the control tube. By this additional means the oscillations are stopped Without any transient effects at the end of an integral number of cycles of oscillation.

These and other objects and aspects of the invention will be apparent to those skilled in the art from the following more detailed description taken in conjunction with the appended drawings, wherein:

Fig. 1 is a circuit diagram of a pulsed oscillator constructed according to the teachings of this invention;

Fig. 2 is a circuit diagram of a modified form of a pulsed oscillator which is characterized in having no transient efiects when the oscillations are stopped; and

Figure 3 is a circuit diagram of a modified portion of the circuit of Fig. 1.

Fig. 1 shows a circuit diagram of an improved pulsed oscillator according to this invention. An input vacuum tube V1 has a cathode connected to ground, a control grid connected thru a grid resistor it) to an input terminal 11, and a plate connected thru a plate resistor 12 to the 13+ terminal of a source of unidirectional potential (not shown). The negative terminal of the source is connected to ground. The plate of input tube V1 is connected thru a voltage divider including resistors 13 and 14 to the negative terminal 15 of a second source of uni-directional potential (not shown). The positive terminal of the second source is connected to ground.

The junction point 16 between voltage divider resistors 13 and 14 is connected to the grid 17 of a control vacuum tube V2. The cathode 18 of tube V2 is connected thru a cathode resistor 19 to the negative terminal 15. A stabilizing vacuum tube V3 includes a cathode 2]. connected thru the common cathode resistor 13 to the negative terminal 15. The control grid 22 of tube V3 is connected to the negative terminal 23 of a source of unidirectional potential. The terminal 23 may be a tap on a voltage divider connected between ground and negative terminal 15. The plate 24 of tube V3 is connected to ground. Tubes V2 and V3 may be electrode structures in a common evacuated envelope or in separate evacuated envelopes.

The plate 25 of control tube V2 is coupled thru a direct current path to a ringing circuit 26. The coupling path may include a resistor 27. The ringing circuit, or table circuit, 26 includes a capacitor 28 and a centertapped inductor 29 connected in parallel. The bottom end 30 of the ringing circuit 26 is connected to ground.

The top end 31 of ringing circuit 26 is coupled thru resistor 27 (which may have a value of Zero ohms), and thru a grid resistor 32 to the control grid 33 of a cathode follower amplifier vacuum tube V4. The cathode 34 or" amplifier tube V4 is connected thru a variable cathode resistor 35 to the center tap on inductor 29. The plate 36 of amplifier tube V4 is connected to the 33+ terminal of a source of uni-directional potential. An output is preferably obtained from the cathode 34 of amplifier tube V4. Alternatively, an output may be obtained from the center tap on inductor 29.

The operation of the circuit of Fig. i will now be described. The grid 33 of cathode follower amplifier tube V4 is coupled to the top end 31 of ringing circuit 25, and the cathode 34 is coupled to the center tap of inductor 29. Resistor 35 is adjusted so that once oscillations are started in the ringing circuit 26, the amplifier tube V4 will' feed'ba'ck sufficient energy into the ringing circuit to maintain the oscillations therein at a constant amplitude. Stated anotherway, the amplifier tube V4 feeds back sufficient energy into ringing circuit 26 to makeup for energy losses within the ringing circuit; The ringing circuit 26 is prevented from oscillating when tube V2 is conductive. When tube V2 is conductive, a constant direct current is drawn from ground, thru inductor 29, thru resistor 27, thru lead 38, thru tube V2, and thru cathode resistor 19 to the negative terminal 15 of the source of unidirectional potential-having its positive terminal connected to ground. The relatively low impedance of the tube V2 and the power supply which are connected in shunt with the ringing circuit 26 effectively damp out or prevent oscillations in the ringing circuit.

When tube V2 is conductive, a steady direct current is drawn thru inductor 29. When tube V2 is cut-01f, the enenergy stored in inductor 29 starts oscillating between the inductor 29 and the capacitor 28 of the ringing circuit. The oscillations are then maintained at a constant ampliture by the action of amplifier tube V4.

The conductivity characteristics of control tube V 2 are controlled by the action of input tube V1 and stabilizing tube V3. When the input signal to input terminal 1. is a negative potential, input tube V1 is cut-ofi and the potential applied from tap 16 on the voltage divider 13, 14 to the grid 17 of control tube V2 is suiiiciently high to render tube V2 conductive. When the input signal applied to input terminal 11 is at ground or a positive potential, tube V1 is rendered conductive and the potential applied from tap 16 to grid 17 of tube V2 is sufficiently low to render tube V2 non-conducting. A moderate decrease in the potential applied to the grid-1 7 of tube V2 is suflicient to cut tube V2 off because the cathode 18 of tube V2ris prevented from falling to the negative potential of negative terminal 15 by reason of'the action of stabil izer tube V3."

The operation of tubes V2 and V3 can be more clearly understood in terms of typical operating voltages. 'With a constant bias of 73 volts applied to grid 22 of tube V3, the potential on cathode 21 (and cathode 18 of tube V2) is prevented from falling below --73 volts due to cathode'follower action. When 86 volts is applied from tap 16 of the voltage divider to grid 17 of tube V2,.tube

V2 is completely'cut-ofi, and tube V3 is conductive. The

cathodes of tubes V2 and V3 are'then at about 73 volts determined by the potential on the grid of .tube V2. When 65 volts is applied from tap 16 to grid 17 of tube V2,.tube V2 is fully conductive causing the cathodes of tubes V2 and V3 to rise from about -73 volts to about 65 volts. Under this condition, tube V3 is completely out off. It is thus apparent that when tube V2 is conductive, tube V3is cut-ofi, and vice versa.

Stabilizing tube V3 prevents the cathode of tube V2 from falling below 73 volts so thata moderatevoltage increase from 86 volts to .65 volts is sufiicient to-render tube V2 conductive. l V i The presence of the relatively large cathode resistor 19 'in the circuit of tube V2 makes the circuit draw a constant current thru inductor-29 when the control tube V2 is conductive. The value'of current drawn does not noticeably decrease as'the tube V2 age's, and it is substantially unaffected by the substitution of one tube V2 for another. By using the stabilizing tube V3, these constant current characteristics in the operation'of tube V2 are obtained without requiring a large negative transition on the grid 17 of tubeVZ to cut the tube ofi,

It is thus far apparent that when tube V2 is conductive, a constant charging current is drawn thru inductor 29 of the ringing circuit 26. When tube V2 is rendered nonconductive, the energy in inductor 29 starts oscillations in the ringing circuit 26 which aremaintainedata' consant amplitude by the action of amplifier tube V4. In order to stop the oscillations in the ringing circuit 26 without traninitially drawn thru inductor 29 by control tube V2 must be equal and opposite to the instantaneous current flowing in inductor 29 due to the oscillations in the ringing circuit 26. Since the amplitude of the first oscillation in ringing circuit 26 is determined by the current drawn by tube V2, and since theamplitude of the. oscillations in ringing tube 26 are maintained substantially constant, the resumption of current flow thru the control tube V2 occurs with a currentv amplitude .of the correct value to provide a transient-freestop of the oscillations. In order to stop the oscillations in ringing circuit 26 with no transient eifects whatsoever, it is additionally necessary to start the drawingof'current thru'the inductor 29 at the instant of the end of an integral number of oscillations in the ringing circuit. This may be accomplished in the circuit of Fig. 1 by means of a feed back timing arrangement (not shown) or maybe accomplished by thefcircuit shown in Fig. 2. V

T hecircuit of Fig. 1 has been found to operate in the desired manner with a direct connection in place of the resistor 27. However, a further improvement in the transient-free stopping of oscillations in the ringing circuit- 26 ispossible by the useof resistor 27- as shown in fig; 1. When tube V2 starts conducting, the current going thru the inductor 29 and the resistor 27 causes a voltage drop in the resistor 27 of such a. polarity-as to reduce the potential on the grid 33 of amplifier tube V4. Amplifier tube V4is thereby inactivated as soon as control tube V2 is rendered conductive. proves the transient-free stopping characteristics of the circuit. 3 v u The control tube V2 controls the presence or absence of oscillations. in ringing circuit 26. When tube V2 is conductive, tube V3 is cut-01f, and vice versa. 'It is therefore'apparent that the oscillations in ringing circuit 26 also may be controlled by applying the signal from tap .16 to the grid-22 of tube V3, and applying the fixed potential of 73 volts tothe grid 17 of tube V2, as shown inFig. 3. In this alternative arrangement, the presence of oscillations in ringing circuit 26 will occur when tube V1 is cut-ofi, rather than when tube V1 is conductive.- v

Fig. 2 shows a modified form of pulsed amplifier including diodes V6 and. V7 interposedin the circuit between the plate of the control tube and the ringing circuit. Circuit elements in Fig. 2 have been given the same numerals with prime designations added as have been given to corresponding'circuit elements in Fig. 1. Fig. 2 does not include the signal input circuit which could be the same as the circuit-of tube V1 in Fig. l. Diodes V6 and V7 have-their respective cathodes. 40 and 41 connectedto the plate 25'of control tube V2. The plate 42 of diode V6 isconnected thru a battery.43 to ground. The plate .44 of diode V7 -is connected to the top=end 31'-of'the ringing circuit 26'. .Battery 43. is poled. toirnake the plate 42 ofdiode V6 negative with respect to ground by'an V amount -such. that: the potential 0115 the. cathodes 4e, 41 isequal to(or slightly negativewith respect to) the potential at the top. end 31 0f the ringing circuit when control tube V2 is conductive. The circuit of Fig. 2 provides an absolutely transient-free stop of the oscillations in ringing circuit 26'. because the current drawn over lead 38' from the ringing'circuit 26'.is started .pre cisely-at the end of an integral numberofcycles of 0scillation in the ringing circuit. 'In. the circuitscf both Figal-and Fig. 2, the polarities are such that thefirst half-cycle ofoscillation in the ringing circuit is .a positive half-cycle followed by a negative half-cycle.

In order to provide an absolutely transient-free stopping of the oscillations in the ringing circuit, current should-start flowing thru lead 38 at the instant following a negative halt-cycle when zero potential exists at the top end 31" of -'ringing circuit 26'.- Battery 43 has a valuesuch' thatth'e cathodes "t0 and 41 of diodesVaS and 'V7 -cannot fall below the slightly negativevalue This further imof the voltage at the top end 31 of ringing circuit 26' when control tube V2 is conductive. If the potential on the cathodes 4t) and 41 should tend to fall below this slightly negative value, current would flow from ground thru battery 43 and thru the inter-electrode space between plate 42 and cathode 49. This current would prevent the potential on cathode 441 from falling below the predetermined value. Current cannot flow from ringing circuit 26' over lead 38 and thru diode V7 unless the potential on the top end 31' of the ringing circuit is equal to or higher than (more positive than) the potential on cathode 41 (the potential on the top end 31' of ringing circuit 26' when control tube V2 is fully conductive). Therefore, if a positive voltage transition is impressed on the grid 17' of control tube V2 during the occurrence of a negative halt-cycle on the top end 31 of ringing circuit 26', control tube V2 cannot draw current from the ringing circuit thru diode V7 until the end of the negative half-cycle on the top end 31' of ringing circuit 26'. In the meantime, control tube V2 draws current from ground thru battery 43 and thru diode V6. Therefore, control tube V2 starts drawing current from ringing circuit 26' at such a time as to completely cancel the oscillations in ringing circuit 26'. By thus limiting the instant at which control tube V2 can start drawing current from ringing circuit 26', transientfree stopping of the oscillations in the ringing circuit is accomplished.

In the use of pulsed oscillators, it is common to provide some degree of synchronism between the duration of the energizing control pulse and the duration of an integral number of oscillations in the ringing circuit. In prior art circuits the two durations must be carefully maintained at values within two or three electrical degrees of the oscillations in order to keep the stopping transients down to reasonable proportions. According to the form of the invention shown in Fig. 2, completely transient-free stopping is achieved when the trailing edge of the control pulse occurs at any time within the 180 electrical degrees of the negative half-cycle on the top end 31 of ringing circuit 26'.

It is thus apparent that the pulsed oscillators of this invention provide oscillations of constant amplitude for any desired period of time depending on the length of the input control pulse. It is also apparent that the constant current control tube circuit is such as to be unafiected by tube aging or tube substitutions. Therefore, frequent adjustments of the circuit are not needed to minimize the transients occurring when the oscillations are stopped. It is further apparent that according to this invention, the oscillations can be stopped without any transient efiect.

What is claimed is:

1. A pulsed oscillator comprising, a ringing circuit including a capacitor and an inductor, an amplifier circuit coupled with said ringing circuit to sustain constant amplitude oscillations therein, a control tube circuit coupled to said ringing circuit to draw a charging direct current thru said inductor when the control tube is conductive, said control tube circuit including a control tube having a grid, a plate coupled to said ringing circuit, and a cathode connected to a stabilizing degenerative cathode resistor, stabilizing tube means to prevent the cathode of said control tube from falling below a predetermnied potential when said control tube is cut-ofi, and means to apply a control signal to the grid of said control tube.

2. A pulsed oscillator as defined in claim 1, wherein said stabilizing tube means comprises, a stabilizing tube including cathode, grid and plate electrodes, and means applying fixed potentials to said grid and said plate, said stabilizing cathode resistor being common to said stabilizing tube and said control tube.

3. A pulsed oscillator as defined in claim 1 wherein said amplifier circuit comprises a vacuum tube including cathode, grid and plate electrodes, means coupling one end of said inductor to said grid, and a variable cathode resistor coupling said cathode to an intermediate point on said inductor.

4. A pulsed oscillator as defined in claim 3, and in addition, a resistor in the path common to the cathode-grid circuit of said amplifier tube and the direct current path of said control tube, whereby the potential developed across said resistor when said control tube starts conducting acts to stop the amplifying action of said amplifier tube.

5. A pulsed oscillator as defined in claim 1 wherein said means to apply a control signal to the grid of said con trol tube comprises, an input vacuum tube including cathode, grid and plate electrodes, voltage divider means coupling the plate of said input tube to the grid of said control tube, and means to apply a control signal to the, grid of said input tube to alternatively render said tubd, conductive and non-conductive.

6. A pulsed oscillator as defined in claim 1, and in addition, first and second diodes each including cathode and plate electrodes, means connecting the cathode of said first diode to the plate of said control tube, means connecting the plate of said first diode to a point of reference potential, and means connecting said second diode in series in the direct current path between said ringing circuit and said control tube, the cathode of said second diode being connected to the plate of said control tube, and the plate of said second diode being connected to said ringing circuit.

7. A pulsed oscillator as defined in claim 1, and in addition, diode means interposed in the direct current path between said ringing circuit and said control tube to prevent the drawing of current from said ringing circuit by said control tube prior to the end of an integral number of oscillations in said ringing circuit.

8. A pulsed oscillator comprising, a ringing circuit in cluding a capacitor and an inductor, an amplifier circuit coupled with said ringing circuit to sustain constant amplitude oscillations therein, a first tube including a cathode, a gird and a plate, said plate being coupled to said ringing circuit to draw a charging direct current thru said inductor when said tube is conductive, a second tube, a com mon cathode impedance for said first and second tubes, means to apply a fixed bias to the grid one of said tubes and means to apply a control signal to the grid of the other of said tubes.

9. A pulsed oscillator as defined in claim 8 wherein said fixed bias is applied to said second tube and said control signal is applied to said first tube.

10. A pulsed oscillator as defined in claim 8 wherein said fixed bias is applied to said first tube and said control signal is applied to said second tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,495,115 Mayer J an. 17, 1950 2,588,924 Hecht Mar. 11, 1952 2,638,548 MacNichol May 12, 1953 2,659,009 Emslie Nov. 10, 1953 

